Tuning apparatus



Dec. 3, 1946. I R, L. HAR EY. 2,411,858

TUNING APPARATUS Filed Feb. 1, 1945 Zhwentox;

obert L Harvey (Ittorneg Patented Dec. 3, 1946 Robert L. Harvey,Princeton,

Radio Corporation of America,

'of Delaware N. J., assignor to 1 a corporation Application February 1,1943,-Serial No. 474,275

This invention relates totuning apparatus for use in radio and analogoussystems for the communication of intelligence and has for its principalobject to provide an improved tuner for use at ultra high frequencies(say, 500-3,000 megacycles) and 'one capable of tuning over a relativelywide band in that selected portion of the frequency spectrum for whichthe apparatus is designed. 7

Another andimportant object of the present invention is to provide aninexpensive yet reliable tuner of the general type described and onecharacterized by its ease of assembly and by the simplicity and economyof its parts.

Certain preferred details of construction, together with other objectsand advantages will be apparent and the invention itself will be bestunderstood by reference to the following specification and to theaccompanying drawing, wherein t Fig. 1 is a longitudinal sectional viewof a tuning apparatus constructed in accordance with the principle ofthe invention and,

Fig. 2 shows, diagrammatically, a circuit which is the electricalequivalent of the tuner of Fig. 1.

The embodiment of the invention which has been selected for purposes ofillustration is made up of but three separable parts, comprising: anopen ended cylinder indicated generally at l and having a bore 2 of auniform diameter which is small with respect to its length, a pistonindicated generally at 5 and which is mounted for slidable movementwithin the bore of the cylinder I, and a wire-like conductor l5 whichextends into the said cylinder through an aperture 3. The cylinder l isconstituted of polystyrene or other preferably moldable insulatingmaterial and is provided with a metalized outer surface 4 which mayconsist of a layer of copper plated over an underlying layer ofevaporated silver (not shown) It will be observed that this metalizedouter surface 4 has an undulate contour, that is to say the cylinderwall is not of uniform thickness, but, as viewed from end to end,comprises a thin-walled portion A, a bulbous portion B, a secondthin-walled portion and a frusto-conical end portion D. If desired thetwo thick walled sections B and D may be of duplicate contour.

The piston 5 comprises two plug-like parts 6 and 1, respectively,connected by a central rod 8 of a length calculated to bring the saidplugs into register,simultaneously, with either the two thin-walledsections A and C or the two thick walled sections B and D. This piston 5may be 4 Claims. (01. 17844) connection (i. e., the film 9) 2-constituted of solid metal but is preferably made of the same insulatingmaterial (e. g., polystyrene) as the cylinder 1 and is provided with ametalized surface 9 which covers both the plugs 6 and 1 and theconnecting rod 8. In either event an insulating shaft I0 is provided .onone end of the piston for adjusting its position within the cylinder I.If desired, each of the plugs 6 and I may be provided with acircumferential flange H which serves to reduce friction and to preventthe metalized surfaces of the plugs from wearing away by contact withthe inner uncoated surface of the cylinder. It will be observed that thediameter of the rod 8 is small with respect to the diameter of the plugsB and 1, hence there is space between the plug into which the wire-likeconductor or loop extends without interfering with the limited degree ofmovement required to bring the said plugs into register with the severalthin-wall and thickwall portions of the cylinder.

Since only the outer surface 4 of the cylinder l is constituted ofmetal, the metal (or metalized) plugs 6 and I of the piston are at alltimes presented in useful capacitive relation with the particularsurface portions of the cylinder with which they are in register. Thevalue of this capacitance is a function of the quantity or thickness ofthe insulating material between the surface 4 and the plugs 6 and 1 atany given moment, hence, the capacitance can be varied by moving thepiston 5 within the bore of the cylinder l. Thus, referring now to Fig.2, one may consider the device of Fig. 1 as comprising two variablecapacitors whose adjustable armatures comprise the movable plugs 6 and1, respectively and whose fixed plates comprise the particular portionsof the metal surface 4 of the cylinder l with which the plugs are inregister at any given moment. Since the plugs 6 and l are connectedtogether by the metalized rod 8, and since the several metalized surfacesections A, B, C and D, of the cylinder are interconnected by the metalwhich extends therebetween it is apparent that these two variablecapacitors 4-6, 4-1, (Fig. 2) are effectively connected in series. Itwill also be apparent that since the series inherently possessesdistributed inductance, the device of the invention in effect comprisesa tuned circuit, which may be inductively coupled, as by means of thewire-like conductor IE to an external circuit. Thus, if the device ofthe invention is incorporated in a radio receiver one end of the loopedconductor 15 may be connected to the antenna and the other end tov oneof the electrodes of a vacuum tube oscillator or amplifier, not shown.

In one successful embodiment of the invention wherein the cylinder I andpiston were constituted of polystyrene, and were of the dimensions givenbelow, the tuner of the invention operated successfully over a frequencyband of 400m 600 megacycles:

Overall length of the cylinder 6" Diameter of its bore 1" Maximum wallthickness 4" Minimum wall thickness 1 Length of piston plugs /2 Lengthof the connecting rod 2" It will be observed that in this typicalinstallation the bore of the cylinder is of a diameter which is smallwith respect to its length, and that the overall length of the piston 5was less than one-half of the wavelength corresponding to the maximumfrequency. Thus, the device of the invention may be said to operate as asection of a coaxial transmission line (rather than as-a waveguide) and,with this fact in mind, it will be apparent that the tuner can bedimensioned to cover substantially any desired frequency band in the"centimeter wave range.

Various modifications of the invention (such for example, as formingtheseveral portions of, the cylinder wall of materials having differentdielectric constants) will suggest themselves to those skilled in theart. Accordingly, the foregoing is to be interpreted as illustrative andnot in a limiting sense except as required by the prior art and by thespirit of the appended claims.

What is claimed is:

1. A tuning device comprising a hollow cylin- 4 der constituted of adielectric material; said cylinder having a body of non-uniformthickness and a bore of substantially uniform diameter; a film-likemetal armature on the outer surface of said cylinder; a core, includinga second armature, mounted for slidable movement on and within theboreof said cylinder whereby said armature and said first mentionedarmature form a capacitor; said armatures possessing capacitance anddistributed inductance of a value calculated to tune said device over apredetermined frequency range, and means presented to the interior ofsaid cylinder for coupling said device to an external circuit.

2. The invention as set forth in claim 1 and wherein said core comprisestwo spaced-apart plugs of a diameter not exceeding the diameter of thebore of said cylinder and an axially extending connecting rod of smallerdiameter, and wherein said coupling means is presented to the spacespanned by said connecting rod.

3. The invention as set forth in claim 1 and wherein the body of saidcylinder comprises alternate thin and thick wall portions and therelative length of the plug and rod portions of said core are such as tobring said plugs into register; simultaneously with similar tions ofsaid cylinder.

4. The invention as set forth in claim. 1 and wherein said "hollowcylinder comprises a plurality of thin wall portions and an intermediateannular bulbous portion, and said first mentioned armature comprises acontinuous metallic de-.

posit covering the outer surface of all of: said cylinder portions.ROBERT L. HARVEY.

alternate wall por-'

